With the development of electronic industry, electronic products have increasingly demanded for high performance, high speed, and compact size. To cope with this trend, there have been developed numerous stacking methods such as stacking a plurality of semiconductor chips on a single substrate or stacking a package on another package. A structure where packages are stacked on one another is called Package-On-Package (POP). There is also an interposer POP structure where an interposer is mounted on a package.